Production of sound-record photographic positives



Oct. 21 1924.

' 1,512,681 J. ENGL PRODUCTION OF SOUND RECORD PHOTOGRAPHIC POSITIVES Filed July 28 1924.

@wur/Moc 90S? aal, A;

. Patented Get. 211, 471924.l

x 'UNITED PATENT, f01:11:,@En. K

Josar ENGL, or nnamnoaunnwatn, Granular, Assioma To 'rar-amok;

Lummen; or zunicn, swmzEataNna coaronarron or. swrrzimLann.

raoDUc'rI'oNor sonnen-.RECORD roroenfarmcfrosrnvns.'

; y Application ltiled. July 28,

To all whom it mayconcem.' l l z .Be it known that I, Josnr ENGL, a citizen of the German Re ublic and resident of y Berlin-Grunewald, ermany, haveinvented certain Vnew and useful `Im rovements, in

the Production -of- Soundecord lPhotographic Positives, of which the Vfollowing 1s a specification. ,l i

y The invention relatestoy the production of` sound @record `photographic positives.` More particularly it relatesvtof a process whereby aphotographic` negative maybe made byacousticallyfvaried light, anda `positive print made frein such `negative bearingaA photographic ,recordof vary-lng intensitiesw'hich may vbe, utilized in the subsequent reproduction ofl sound,` therefrom. An object of vthe `ir 1ve'ntion.. is the produc'- tion of ay process involvingV the makingof the ne ative and. therefrom the positive photograp ic record, in such a .manner that certain `inaccuracies of, thefphotographic steps maybe obviated;` anrdthat thereby, when sound is reproducedby theutilization of thefpositivet will correspond quite accurately to the acoustically-yaried 1 light distortions which mightarise becauseofin-Y accuracies ofthe photographicprocess.

50 A, It Vshouldbe understoodthat the photographic i process .comprising this invention may comprise`V part oi. .a completeaprocess orsystem for recording. and subsequently reproducing 4sound, which sound vibrations .to be reproduced are directed to `a form of micro hone @whereby j` an y electrical current is Vpro uced4 whichg varies in correspondenc'e Withthe soundvibrations which producedthe same. VThis current flows in 40 a circuit Whichincludes ,arecordin lamp,l

the light of whichfallsiipon a suita le sensitiaed` surface, such 'as a film strip 1' which is moved across the beamizoflight. ,This recording ,light is maintained at constant luminosity when .no sound- Waves are 'affect-A ing the micro `hone, and its intensity varies above and be ovv this constant, or average, luminosity Whensoundfvibrations act upon f the microphone. lAccordingly, when the negative isthus made, on theilm anddef` veloped and a positive print .madel there-` from', the sound record "should appear on the `latter in the form of lines offvarying density. 'Whenthe ysound/isi.subs equently 'u to be reproduced, the rpositive filml is fed jproductionof sound m' 1924. serial mi. 728,534.

pastabonstanty source of light which'passes through rthe ilmto greater or less extent in accordance .with 4.the varying densities ,of

the sound, record linesor imaves thereon,

the light thus passing through the film 4falling upon a light-sensitive device, such `as a` photo-electric cell. Electrical currents, whlchvaryin corres Vondence withthe light falling upon` the p oteIectric cell, will thereby be set up and 'these electrical currents may be ledto some form of loud speak,- er, orv sound reproducingdevice, whereby sound vibrations may be generated,and these 4.fd'iouldf of course. corres ond as closely. as possible toy the ori inai) sound vibrations which Were'receive by the microphone in the recording process. Q

iIn carr ing out such a process,r however,

problems ave arisen.. in the em loyment of the properties ofl-the1sensitive m as to the reactions of they latter' to varying' light intensities,.1n such mannerthat there shall be nolinaccuracies in thephotographic .recording .,steps.. ,The varyingrintensity of` the light, by whichgthe -`negatives are-made may I l y bemade toI corresp ond ;quite closely tothe used for producing the negative, lWithout original soundvibrations, and the final rebemade to correspondquite closely tothe variationsof current vproduced `:by` the i yvariations' -of `light passing through'lthe positive film.v and falling upon thel photoelectric`.cell; but the pierfections of `process byvwhich these resalts/are attained `will beto a, considerable extent nullified if, substantial inaccuracies arefallowed tolenter the completeivsystem because of the inaccuracies which appear tin monly practiced.

In the problem,the

the photographic steps4 as the same are comsolution 'of herein attained, there areftwo;` factors ywhichl Inustbe considered.. First, there. should be an `apprnximately constant proportion v between the-intensity of luminosity of the re cordinglight by Whichthe negative is made and the intensity of the light which passes through the' positive film and falls upon the photocellfin the sound reproduction process.

The second factor to beconsider'ed isfthe desirabilit of having as great a part as possible o the positive film, or record, com paratively transparent, or as little light-ab.- so-rptive as possible, vbecause the;- loudness of the reproduction of `sonnd'by' the loud .speaker will vary in accordance with the f5, after.- The invention consists in the procamount *of light which passes through the positive.v film, and'acts upon the photo-cell.

This can bcaccomplished when the transparency of the positive record-bearing film, or conversely, .lts light-absorl'itive power.

has l`a possible range between zero and ,100'

percent. This ivlll be so when portions of the positive-,film corresponding tof-average intensity of the recording light have such a density that they will absorb 50 `per p tout of the light', falling upon the same in tions, and vary from approximately zero to approximately 100 per cent; flVith this arrangement the entire range of sounds may berecorded, andpalso a great' part of the film willgbe-o'f large transparency.

Considering' the light which isv to act upon the Vphoto-cell, in' sound reproduction, Aas passing through a film-of transparent material, Celluloid vor vthe like, bearing photographic images of varying darkness, the celluloid or other base i's`considered as entirely transparent 'and thev light-absorptive properties-of the film are consideredas depending entirely uponv tm varying density of the photographic sound record thereon. If this condition vis realized, namely that thek absorption ofthe positive 4film shall be approximately fifty per cent of the ylight falling thereon when zero sound is to be reproduced, it-follows that the light` passing through the positive film upon 'the photocell, during y reproduction, may: vary p throughout the 'entire' range of intensity of the 'acousticallyvaried vrecording lamp by which the negatives were made.

l These "conditionscan only be fulfilled by i lspecial steps inthe photographic process;

this because of the'f'act that the variations of density'in the negative, and the positive,

. are not strictly proportional, with'norma'l development, to variations in the intensity kof the recordinglight.- This is particularly so where the illuminating intensity is small, corresponding to al vlarge degree of transparency of th'epositive. In accordance with this invention 'these desired conditions are fulfilled by? developing'the negative in a special Way,'and making the positive print in 'a specialfway, as will be disclosed hereess, and steps thereof hereinafter more fully setforth and particularly pointed out in the appended claims.

The difficulties to be overcome, and the means by which the)v are overcome, in accordance. with this` lnvention, will be best understood by consideration of the accompanying drawings forming part of this application. In the drawin Fig. 1 is a-oharacteristic curve illustrating the manner in which the density of a negative varies for varying intensities of the recording light, with normaldevelopment,`and also illustrating the manner in which the density of a positive varies for varying intensities of the light passing through a negative and falling upon the ositive, in con-` tact'printing, with normal evelopment, the general form of the curve being the same in both instances', the ordinate representing logarithms of opacity and the abscissa representing logarithms of intensity, it being the common practicev to use logarithmic values in making such curves;

Fig. 2 is a diagram illustrating in full line, the relation between the light assing through the positive film in repro uction and the intensity of the recordin light in making the negative, when the diensity of the print varies as in Fig. 1, and in dash line, the relation when this invention is practiced, and

Fig.v 3 is a diagram representing variation in the opacity of the negative as a function vof. the intensity of the recording light, for` varying times'of development, by the aid'of which the problems referred to may be solved. One of the diiculties of the problem is made apparent-byV consideration of Fig. 1. Obviously, ifthe density, or intensity` of the effect upon the negative or the positive increased proportionately to the increase in the illuminating intensity, the characteristic curve representing this relation would be a straight line, which might, fory example, start at the junction of the ordinate and the abscissa of the diagram and form an angle of 45 with each. Such a linear relation to 'the variations "in light -intensity and blackening of the film would represent true proportionality between the two. The coatings of 'photographic light sensitive films. or plates, do not, however, with normal development, vary in this desiredv manner, and in all photographic emulsions or coatings with' which "I am familiar the eiect of constantly increasing the intensity of light' is the production'of density or intensity of marking on the'film which varies disproportionatelyy to the illuminating intensity, I

as shown by the curve in Fig. 1, this figure representing in itsgen'eral form the characteristic of all emulsions under these conditions. Itwill be noted that the characteristic curve A (Fig.`-.1)-has a lower portion 1, illustrated in dash in Fig. 1, which ,is concave upwards, this 'corresponding to the ,lower illuminating intensities. "From this y.point .the curve has anv approximately straight upwardly inclined .portion in which there is an approximately'constant relation between the illuminating intensity and the density orfintensity prod ucedthereby on the lm.` This portion; of the ,curveis succeeded bya downwardly concaved portion3,.which is approaching theihorizontal. y'Referring to Fig.V 1 it is'evident that when one is3working on the lower curved part 1 ofthe characteristic. curve there is .sa 'very considerable lack of proportionality between the illuminating intensity yand the density or "degree of blackeningv produced on the print. This condition corresponds, `of course, to a comparatively small illuminating intensity and `also to a rather small degree ofblackening ofthe film whichcorresponds to less than 50 per cent-of absorption` whenlight is subsequently l passed through the print in'reproducing-the sound.

There is a linear proportion betweenthe illuminating intensity and the densityor degree of blackening when one operates on they straight vvline portion 2 of the characteristie curve since y this isalmostl a` straight line. y It is not .'possible,` however, `to work only v.on the straight 1 lineaportion 2 ofv the curve, if `the second vof thetwo factors. of the problem noted above is to be fulfilled sinoethe lower curved `part l of the curve corresponds to a large `degree .of transparency of the print, which as `stated above, shouldbe attained; Y f

In Fig. 2 `themcurve Brepresents the 'relation` between the light-passing through the positive filml in reproduction vand the intensity of the recording.lightiinglmaking the` negative,.when the negatives4 has been made by a vrecording light varying between the same limits as inFig. 1, and when the` developmentof the negativel and positive has been normal, the same as in Fig. 1. IIn Fig.. 2 ,thewabscissa represents` the varying intensity of the recording. light, and the ordinate represents the proportion of light from `zero percent to 100 percent passing throughthe positive film. If there were a proper proportionL between the `factors represented by the ordinate'and the abscissa,

, y the curve B would be a straightv line. Curve Bg however, departs from the required straight ,line to aconsiderable extent,H almost the whole of this curve bein-gl concave downwards. .This 4curve B is curved in the manner shown because of the curved nature of the characteristic curves A, asshown in Fignfl, forboth ositive and negativeilms. That vis to say', t et disproportionalities producedfin. making the negative-and in printing the'jpositive, with norm-a1.v development,

are added together, in etl'ect to produce a curve such as B in Fig. 2, the curves shown all being determined experimentally.

They two desirable'tactors can, however, be fulfilled and ani-approximately.straight line, proportional Irelation. vestablished betweenthe intensity of they recording light and the proportionzrof light passing through the positiveglilnr in'. reproduction by steps which will now be described'as a result of whichthe approximately straight lineB1 maybe substituted for. the concave curve B in Fig. 2. yOn referring to Fig. 3 it is seen 'that the opacity of the negative as a function of the intensity of the recording light depends upon the length of time of development of the.y negative. In this figure the curves C1, C2 and'C3 -representthe relation between the opacity of the negative and the intensityof the recording light for development times of ten minutes, twenty minutes and` thirty minutes respectively. vIt is evident that with increasing timefof development, with the same bath, the curves become increasingly steep inthe upper portions of the. saine.` It will be notedv that the upper #portions of these curves vcorrespond to considerable opacity of thenegative; accordingly to `considerable transparency .of ,the positive.v By .suitable choice of an abnormallylong time of development the den: sity of the negative lilm may 'be so` altered .that the corresponding curve for `the positive ilm is approximately straight. The requisite steepness of thecurve, such as curve C, in Fig. `3, may bev expressed mathematically. Calling the opacity of the negative lfilm coatin O, the incident lightr Land the light whlch passesthrough the aimxT, um 0% TheA relation between opacity `O and the `incident `light L is given by the equation O=.La .where a is a constant known as the index oit'. gradation, which depends` upon the. time taken for Vdevelopment, on thev nature of the sensitive lmand on.the developer used. This `relation has been. developed by experimental .i photographic chemistry. f i For negative iilms ascommonly'lnade and developed the value of a is not greater than 0.5. In accordance with the present invention the development -must .be carried so far that a isl greater than 1, a value of 1 for the constant @corresponding to astraight line, making an angle ofnll-with theabscis'sa. Ita isgreater than 1, `the curve, such as C2 or C3, willdepart somewhat from a straight line, and the -steepness of such curve, will, ofcourse, be greater than 45, at all points lthereof, and suchv a condition corresponds to greater opacity of the i negative. and, therefore, to greater transparency of= the positive;

In actual practice-'the negative is developed for an abnormally long time, which may, forexample, be between twenty and twenty-five minutes with: normal intensity of bath. The negative film thus overdeveloped is naturally very dense all over. It is advisable-touse Ia developer which produces as lar e contrast as possible, i. e. one which acts arshl It is also advisable to use developers which have but little tendency to fog, 4and if desired, known means for preventing-fogging may be used.

The negative -havmg been developed and fixedand washed'in the usual wa the positive is made therefrom preferab y by con-` tact printing. Adjustments are made of the variousfactors concerned in printing such that the portions of the positive print which corres ond to the average intensity of the recor lngy light used -in making the negative shallbe approximately 50 er cent, as has been explalned above. T is may be accomplishedby regulatin the intensity of the source of li htused or printin or by .adjusting the time of printing, or t e time of' development of the rint, or the intensity of the bath used in eveloping the print.

It is advisable that the development lof the Y plrint be normal, in order to obtain freedom omfogging, as much as possible. vTherefore, the most ractical means of adjusting consists in adjusting the ,intensity'of the printing li ht. The' time of printing might, of course, e varied, as stated above, but it is notpractical to vary this time toa great extent, particularly since it is,.of course, desirable toobtain as great an output in feet of film per day as ossible.

'- It may be advisa le to describe themanner inwhich the printing lighti'sso regulatedas to give a transparency of per,

cent to the positive film at. points corresponding to average intensity of the recording lightl used in making the negative. A .transparent-stripoflm having no photographic record thereon, is interposed betweentheconstant source of light which is used in reproducing, and the photo-electric cell. The current then produced by the photo-elefctric cell is-measured and is considered as 100 er cent. Various strips of film are then ta en 'as samples and on each of the same-a negative is made corresponding to average intensity of recordinglight. yThat is to say, the recording light is' allowed to act upon these strips of negative filmwheu no sound vibrations are affecting the circuit of the recordinglight, so that this light accordingly is at its constant average value.

tive strips are then developed in the or inary way, and a print is made from one yof the same with an intensity of printing-'light which may be as close to the necessary intensity as can be guessed at. The printthus made `is then interposed. between the .constant reproducing light source and the photo-electric cell, and the -to cell in reproducing will vary in current produced by the cell is measured. If the current is less than 50 per cent of that previously obtained, it appears that the intensity of printing light was too great, since the photocell current is in quite exact proportion to the intensit of light passing through the film and falling thereupon. Therefore, in rinting from the next sample n ative t e printing intensity will be reduce somewhat and by this cut and t method a printing light intensity may rea ily be obtained, after a few tries, in which the photo cell current will be vfound to be approximately 50 per cent of the current produced when there was no blackening of the film.

Having the intensit of printing light adjusted to the desire int, it 1s evident that the sound intensities which will be printed will vary equally above and below the average intensity of printing which cor responds to zero sound; therefore, the light absorptive properties of the lm will vary throu h a range extending equally below and a ove 50 per cent, this range having only, the adjustment of the time of print' time of development and intensit of bat will be an adjustment at normal res.

The ne' ative produced b the ormai time of evelopment, as escribed, has a density distribution which in fact is a completely distorted record of the real light values. This distortion, however, counteracts the distortion inthe positive re resented by curve B in Fig'. 2. The resul therefore, is `the reduction Aof a condition represented by,t e curve or line Bin 2, representin an almost linear relation between the mtensity of the recording li t and the light assing through the positive film in repro uction. This is, ofcourse, the desired end of the invention, the purpose of which is to produce a succession of images of'sound intensities which may suhsequently b'e used in the reproduction of sound as described above, with the result that the light transmitted by the positive will vary quite exactly with the intensity' of the recordin rlight used in making the negative. There ore, the current produced by the phoquite exact correspondence with the uctuating,

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acoustically varied, current which fed the recording lamp in making the negatives. There would, of course, be no such correspondence between the recording light and the light passing through the positive if such. Steps as have been described were not employed. It should also be carefully noted that the process permits the use of intensities of density upon the film ranging from practically zero to 100 per cent, and that the density corresponding to small electrical currents, or low intensities of the recording light, could not be made bythe common methods without involving considerable distortions of the light effect produced upon the photo cell.

What I claim is:

l. A process of producing positive photographic sound records, comprising maintaining the intensity of a recording light approximately constant, when the same is not afected by sound, acoustically-varying the light above and below such constant or average intensity, causing such acoustically-varied light to fall upon a sensitized surface, developing the negative thus produced to such a degree of density that the inde-x of dation is greater than 1, and printing rom said negative upon a suitable sensitized surface in such a manner, by adjusting the printing light intensity used, that the print, at points thereof corresponding to the average intensity of the said acoustically-varied recording li ht, will absorb approximately one-half of t e light which subsequently will fall thereupon in the utilization of said print in reproducing sound therefrom.

2. A process of producing positive photographicl sound records, comprisingmaintaining the'z'intensity of a recording light approximately constant, when the same is not affected by-sound, austically-varying the light above and below such constant or average intensity, causing such acousticallyvaried light to fall upon a sensitized surface, developing the ne ative thus produced to -such a degree of c ensity that the index of gradation is greater than l, and makin()r a print from said negative upon a suita le sensitized surface with adjustment of the printing light intensity used, the time of printing, time of development and intensity of bath, such that the print, at points thereof corresponding to the average intensity of the said acoustically-varied recording light, will absorb approximately one-half of the light which subsequently will fall thereupon in the utilization of said print in reproducing sound therefrom.

3. A process of producing positive photographic sound records, comprising maintaining the intensity of a recording light approximately constant, when the sameis not affected by sound, acoustically-varying the light above and below such constant or average intensity, causing such acousticallyvarled light to fall upon a sensitized strip with relative movement between the light and strip, to produce a negative which, when developed, will comprise successive images of varying density, overdeveloping the negative to an abnormal extent, and making a print, portions of which are quite transparent, from said negative, upon a sensitized member with transparent base, by adjustment of the printing light intensity used, the time of printing, time of development and intensity of bath, such thatA the print will have light-absorptive properties upon different parts thereof, when subsequently subjected to light, which will vary upwards from a ligure considerably below 50 per cent to a figure above 50 per cent.

In testimony whereof I have signed my name to this specilication.

JOSEF ENGL. 

